Implicit and Explicit Representations of Hand Position in Tool Use

Abstract

Understanding the interactions of visual and proprioceptive information in tool use is important as it is the basis for learning of the tool's kinematic transformation and thus skilled performance. This study investigated how the CNS combines seen cursor positions and felt hand positions under a visuo-motor rotation paradigm. Young and older adult participants performed aiming movements on a digitizer while looking at rotated visual feedback on a monitor. After each movement, they judged either the proprioceptively sensed hand direction or the visually sensed cursor direction. We identified asymmetric mutual biases with a strong visual dominance. Furthermore, we found a number of differences between explicit and implicit judgments of hand directions. The explicit judgments had considerably larger variability than the implicit judgments. The bias toward the cursor direction for the explicit judgments was about twice as strong as for the implicit judgments. The individual biases of explicit and implicit judgments were uncorrelated. Biases of these judgments exhibited opposite sequential effects. Moreover, age-related changes were also different between these judgments. The judgment variability was decreased and the bias toward the cursor direction was increased with increasing age only for the explicit judgments. These results indicate distinct explicit and implicit neural representations of hand direction, similar to the notion of distinct visual systems.

Kinematic cross‐correlation induces sensory integration across separate objects

“…Recent studies have shown that, in a basic cursor‐control task, the perceived position of the hand (cursor) is attracted to the position of the cursor (hand) as mapped onto the same plane of motion (Ladwig et al ., , ; Rand & Heuer, , ; Kirsch et al ., ). We previously found that this perceptual attraction between kinematically related hand and cursor ‘objects’ is consistent with optimal multisensory integration model predictions (Debats et al ., ).…”

“…That is, the perceived position of the hand (in the horizontal plane) is biased to where the cursor (in the frontal plane) would be if mapped onto the same plane of motion, and vice versa. This effect is observed both when there is a slight discrepancy in the hand and cursor movement directions (Rand & Heuer, , ; Debats et al ., ) and in the movement amplitudes (Ladwig et al ., , ; Kirsch et al ., ). In a recent study, we found that the relative strength of these perceptual attraction biases varies with the relative reliability of unimodal hand and cursor position estimates, consistent with optimal‐integration model predictions (Debats et al ., ).…”

“…We used our previous experimental procedure (Debats et al ., ; cf. Rand & Heuer, , ) in which participants made out‐and‐back movements with their right hand between the centre of a semicircular workspace and its boundary. The outward hand movement on the horizontal plane was accompanied by the corresponding motion of a cursor – a little dot – on the frontoparallel monitor.…”

Visual and proprioceptive recalibrations after exposure to a visuomotor rotation

“…In addition to the direct (or explicit) measure, we use an indirect measure in the present study. This is because we have identified some variables that differently affect these measures in our previous studies on multisensory integration (Rand & Heuer, , , , ). For example, aging (Rand & Heuer, ), an enhanced proprioceptive information at the endpoint of the center‐out movement (Rand & Heuer, ), and a preceding adaptation to a visuomotor rotation (Rand & Heuer, ) are among the variables that differentially affect the two types of measure.…”

“…This is because we have identified some variables that differently affect these measures in our previous studies on multisensory integration (Rand & Heuer, , , , ). For example, aging (Rand & Heuer, ), an enhanced proprioceptive information at the endpoint of the center‐out movement (Rand & Heuer, ), and a preceding adaptation to a visuomotor rotation (Rand & Heuer, ) are among the variables that differentially affect the two types of measure. These findings can be taken to suggest the existence of two distinct representations of hand positions, one serving perception and the other one serving action or motor control (e.g., De Vignemont, ; Dijkerman & de Haan, ).…”